Plasmodium (Malaria) species inhabit defined geographical areas, evolve, speciate and undergo short term and historical movement, just as do more complex animal species. The study's objectives are to describe the distribution, epidemiology and population characteristics of the principal species of plasmodia found in lizards of Colombia. Previous work in California followed by a nearly complete 12-month study on the epidemiology and population pattern of malarial parasites in reptiles near Cali, provides a good perspective for a study of other reported malarial parasites of reptiles. The proposed research will include: (a) a continuing faunal survey to discover and describe the principal malarial parasites of reptile populations of different New World life zones, enlisting the aid of collaborating herpetologists whenever possible, (b) life cycle studies, emphasizing transmission, pathology, seasonal dynamics and the occurrence of relapses in relation to host reproductive cycles, (c) a description of the Plasmodium population structure-patterns and an attempt to relate them to host population dynamics, and (d) an examination of the distribution and relationships of malarial parasites in selected reptile groups whose zoogeographic history appears well known already or is currently under active investigation.